U.S. Pat. No. 5,015,492 to Venkatesan and Wu, issued May 14, 1991, herein fully incorporated by reference, disclosed a vapor deposition method and apparatus for coating a substrate with a thin layer of a complex material having a predetermined stoichiometric set of constituents. A pellet of the complex material was irradiated with, for example, a pulsed laser to produce a vapor plume of the complex material. A substrate was exposed to the plume to form the thin layer. The stoichiometry of the thin layer was essentially the same as the stoichiometry of the pellet.
U.S. Pat. No. 5,151,110 to Bein, Brown, Frye, and Brinker, issued Sep. 29, 1992, herein fully incorporated by reference, disclosed a sensor based on a piezoelectric substrate having a coating. The coating included a zeolite and a binder. The binder was needed to bind the zeolite to the piezoelectric substrate. The zeolite had a pore structure of substantially uniform pore diameters. The zeolite absorbed a specific chemical which could enter these pores but did not absorb a different chemical which could not enter these pores. If a specific chemical was absorbed by the zeolite, then the coating was heavier. The heavier coating was detected by the piezoelectric substrate.
The sensor of U.S. Pat. No. 5,151,110 was an important advance in the art but it was subject to an interference if the binder absorbed a chemical or if the binder tended to block the pores of the zeolite. It would be an advance in the zeolite coated piezoelectric substrate sensor art if a means could be found to form a zeolite coating on a piezoelectric substrate without a binder.